Method and apparatus for ascertaining the focus of reflectors



July 13, 1943. J, WESTERLUND 2,324,449

METHOD AND APPARATUS FOR ASCERTAINING THE FOCUS 0F REFLECTORS Filed Aug. 24, 1939 2 Sheets-Sheet 1 54 30 3 l6 1 5 5 g A; 43 3/ 0 [9 O ,8 w 27% 28 -35 e 3 L 3 III Inventor:

Einar J. Westeriund His ttorneg.

July 13, 1943.

Filed Aug. 24, 1939 PHOTO CL L E. J. WESTERLUND METHOD AND APPARATUS FOR ASCERTAINING THE FOCUS OF REFLEGTORS 2 Sheets-Sheet 2 PHOTO-CELL Inventor Elna? J. Westerlund,

His ttorneg UNirEof S A human, 13.1,...

liIETHOD AND APPARATUS roa AscEa'rAni mc rm: FOCUS or nnmc'roas a Elna r John Westerlund, Warren, Ohio, assignor to General Electric Companma corporation of.

New York Application August 24, 1939, semi nazauzz- 10 Claims. 88-14) My invention relates to methods and apparatus for ascertaining very accurately the focus of a reflector, and is particularly useful for determining the proper position to locate a light source the finding of the focus, the equivalent focus,

in a reflector forming part of a light projecton' Still more particularly, my invention relates to or the optimum point for the light source in athereof.

For the proper distribution of thelight from 'a projector and the 'efflcient use thereof, the ngnt projection reflector of revolution or modification point therein at which the light source can be mounted to produce the light beam desired. Once the focus is determined, the light source can .be mounted thereat or with relationjthereto, whereas the determination of any other point for, the j light source assures only that a light beamcorresponding to that directed onto the concentratlng reflector during the test will be projected source must be located accuratelywith respect to the reflector thereof. Heretofore, a removable incandescent lamp served as the light source and inaccuracies of manufacture were compen-' sated for either by optically positioning the ills.-

.mentary light source with respect to the base of the lamp during manufacture or by adjustment of the lamp in and out'of the projection reflector usually by visual examination of the projected pattern of the light beam; In both cases, inaccuracies in the reflector and in the mounting of the lamp were notfully compensated for, and

improved projectors have therefore been devised -in which the light source is permanently mounted in combination with the reflector to avoid all former disadvantages. Lamps of this type take two forms, one, in which an ordinary incandescent lamp is fastened permanently to the reflector in the proper position, and a second, in which the reflector is included in the construction of the lamp as disclosed in Patent 2,148,314, D.'K.

The principal object of my invention is to determine optically the proper position for the light source in a projecting reflector prior to the mounting of a light source therein. -The method must take into account all variations and inaccuracies of manufacture so that the light source can be located at the best possible position in the reflector for the results desired.

Another object of my invention is to provide a method and apparatus for determinin the point of concentration of the light redirected by a projecting reflector when a'controlled beam is directed thereon. This method of operation permits determination of either the iocus'or another thereby upon operation of said light source.

Another object of my invention is to provide a a method and apparatus for measuring the concentration of light along the axis of a c'oncentr'ats beamis diing reflector when a controlled light rected thereinto.

of methods of operation comprising my invention and from the drawings.

vIn the drawings, Fig. .1 is a vertical section through the center of one'specie's of testing ap-' paratus comprising m invention: Fig. 2 is a plan v view of a reflector positioning portion of said apparatus; Fig. 3 is a plan view of'a photo-cell supporting and moving portion thereof; Fig. i

is a perspective view of a photo-cell'and holding means therefor; Figs. 5 and 6 are'perspective views of modified photo-cells for use with the apparatus; and Figs. '1 and 8 are diagrammatic views of-other modifications of apparatus comprising my invention.

To operate the species-of my apparatus shown in Figs. 1 to 4 inclusive, the light projecting reflector Ill is first inserted therein and positioned so that it is'level and centered in the apparatus.

The reflector l0 ln the instance shownis a type forming part of the lamp disclosed in the Wright patent hereinbefore referred to in that it is made of pressed glass having an extremely accurately formed interior surface with a' reflecting coating ll thereon. At the time of insertion, the holder I2 is at a lower position than shown and the re flector I0 is inserted under the leveling ring I 3 and moved upward until the shoulder II which bears a definite relation to the reflecting surface, is brought into engagement with said leveling ring l3.

It is also preferred that the reflector Ill be turned so that the protuberance l5 (Figs. 1 and 2) at a point adjacent the rim thereof is carried against the end of the finger it which is held by the leveling ring l3 so that said reflector [0* also assumes a-deflnite angular relation to the apparatus. The flnger I6 is pivoted on 'the pin I! carried by the leveling ring l3 so that it will move upward and allow the protuberance to pass 3 Further objects and advantages of my inverttion will appear from the following description.

into position if the reflector II is turned counterclockwise and isso weighted as to fall back into position when the protuberance ll passes from under it.

The leveling ring I! engages corresponding vertical guide ways at opposite sides of the vertically extending portion is of the stationary bracket is through the ball bearings as shown in Fig. 2 and, at the moment the reflector III is inserted, is positioned by the flange II which 3 1 assasso reflector ll.

in detail in Pig. 4 are formed by cutting the light rests on the top of said bracket is. The holder I2 is now raised manually until the pin 22 carried by the bracket it enters a hole in the supporting rod 23 therefor, and the rollers 24 on the three equidistantly spaced arms 24' of the ring 2| are against the bottom of the reflector Iii. The ring 25 rests on three springs "carried by the collar 2-1 attached to the upper end of the rod 23 and it and hold the rollers 29 at exactly one level and the same distance from a vertical axis through the apparatus so that the reflector I! is automatically positioned vertically and centralized therein. The bracket 3i engages the vertical slide ways on opposite sides of the vertical portion it of the bracket is through the ball bearlugs 32 as shown in Fig. 2 and takes a vertical position governed by the rod 33 which screws intothe base of said bracket is and which engages lugs 34- of said bracket 3i through the collars 35 and 36.

' sensitive coating on the comparatively narrow (55 inch) metal block 42 with a very sharp tool and are.connected in series due to the conductive properties thereof so that the-electric current generated by each counteracts that of the other and current flows only whenone photo-cell generates more current than the other. The photocells 4| and 4! are mounted on the end of the spindle I which is held by the ball hearings in the hub 44 in a position determined by the slide II in the ways of the bracket 46 which is attached to said ub'ss through the ring 41 and spokes ll. The slide ll is positioned by the adjusting screw which bears against the bracket is and is preferably counterbalanced so that it and the photo cells'll and ll are easily adjusted vertically. The spindle is is rotated. to'cause the photo-cells ll and ll to pick up light from all sides of the reflector II in a uniform manner. bythe electric motor I. which is mounted on the slide .ss through the bracket s1 and which oper- In alignment with the reflector I0 and preferv ably at some distanceiflve feet in this particular;

instance) therefrom is mounted a light projector s1 directing downward and into the reflector iii a lightbeam 39 of parallel rays as indicated. The

.ates said spindle l8 throughthe usual form of speed reducer I2 incorporated therewith, the pulleys 53 and I4 and the belt II. By prior'calibration of the apparatus, the markings on the head of the adjusting screw is when compared with the pointer It and other markings (not shown) on' the slide 45 and the bracket 'indicatethe osition of the separation between the photocells It and H in the reflector ll when the bracket II of the vertically positioning means is at a predetermined position.

[When the'reflector i0 isflrstinseried-into-the apparatus, the photo-cells ll and Ii are most likely oil position vertically and one or the other -is receiving morelight and causing a flow of cur- I rent in the circuit in which they are connected. The connections are made to the terminals of each of the photo-cells I. and I through the metal bands 51 which lie ina channel in the semicircular insulating blocks 58 located in grooves in the spindle ll and which engage'the special solid metal contact strips on the photo-cells through the screws 59. The bands 51 are conlight beam 38 upon striking the reflecting surface II, is redirected toward the focus thereof I as said surface is parabolic, and it is the accurate determination of this point that is the principal function of my apparatus-in this particular instance. By spacing the light projector 31 some distance from the reflector ll, verylittle of the uncontrolled light from the fllament 39 thereof reaches said reflector iii. If a differently shaped reflecting surface is to be examined, it is usually preferred that a different light beam correspond ing to that which will ultimately be projected thereby be directed into the reflector i0 along the light projection axis thereof by the projector :1. The beam projected into the reflector Ill must be angularly similar to the beam which the said reflector I0 is capable of projecting but opposite in direction. In some instances, the said projector may have to be mounted at a different distance from the reflector I0 and a lens may possibly have to be interposed therebetween to produce the light beam required.

The determination of the focus or other point of concentration of the light in the reflector II is made with the aid ofthe finding apparatus shown in Figs. 1 and 3. This apparatus in this instance supports the photo-cells l0 and ll which are arranged one above the other with their light sensitive faces on the axis of projection of the i'nected through insulated wires extending upward through a slot in the spindle 43 to the mercury pools 60 and Bi in'a commutator which-is comprised of the cup portion 82 on the-upper end of said spindle l3 and the stationary cap 63 rested thereon. Both the cup portion 02 and the cap.

63 are made from insulating material and the circuit therethrough is made through the wires 04 and BI (Fig. '3) carried by the cap 63 which dip into the mercury pools i0 and ti respectively, asill which are connected to the screws I! extending from opposite sides thereof. The circuit to the galvanometer 61, which is mounted adjacent the finding apparatus, is made through'the downwardly extending helical springs 68 which hang from the screws 86, the metal arms 80 which are attachedto the insulating block 10 on the slide II and the wiresli. The springs I and the arms 89 also function as a holding meansfor the cap 63 of the commutator to keep it from turning.

Any displacement of the photo-cells 40 and II is indicated by a right or left deflection of the rect location, like amounts of'light fall on each and the galvanometer shows no deflection in ei er direction. This position of the photo-cells The photo-cells" u and il as shown y [,1 rm: is and u is indicatcdbymarking's hereinbefors referred to whichcsn be set up so as to give the distance vertically between said position and a:

reference point such as the ends of the'metal) leads "I! on the reflector II or the shoulder I4 thereof, for instance. In some instances, it may be more desirable to adjust the reflector ill with respect to the photo-cells II and 4| and in such instances the adjustment ismade by turning the knob 13 on the end of the rod SI. The position of the reflector III is then indicated by comparing markings on the collar ll and thelug ll of. bracket II and other markings (not shownr'on the bracket 8| and bracket ll. finding apparatus in the path of the light beam 3 ter of an opening ll'ins second opaque screen It dividing the reflecting surface ll in half. and the photo-cell Ills mounted behind the round opaque screen if and the opening II in position to invtercept the'light passing therebetween.

flector is explored by moving thescreens l2 and The re- II in and out of the reflector along the axis thereof until the least amount'of light falls on' the Allpartsl-ofthe 1 38, such-as the hub 44, spokes II and the rin 41 are provided with a dull black finish to prevent uncontrolled reflection of the light'of said beam 88. After the determination oi the point of concentration of the reflected light, the'reiiector ll istaken from the apparatus by first pulling the pin 22 from the hole in the rod 23 against the photo-cell. '80 as indicated by the miiliammeter ll attached thereto, at which time the screen I! is at the concentration point of the light. At other times when the screen If is oil position,

the light passing through this point enters the opening ll in-thescreen II and falls on the photo-cell I. Th purpose of the screen I! is to prevent stray uncontrolled light from falling on the photo-cell 00. A slide, such as shown at ll, as well as the positioning apparatus shown in -l"ig. Lean ,be used to support the screens l2 and I3 and the reflecting surface II respectively, if desired. One test of a reflecting surface by this I I modification of my invention is usually not repressure of the spring" then allowing the holder l2 and the reflector II to drop clear.

The markings of the flndin'g apparatus can be" calibrated sothat the focus or point of concentration of the reflected light with respect to Y the various parts thereof engaged by 'the' positioning Once the focus or point of concentration of the reflected light is determined,

' the light source can easily be positioned at said point or at a given relation thereto. To do this it may be necessary to mount the reflector in a holdermuch the same as in the iinding uppers-- tus, but in place of the photo-cells have a pointeror other indicating means which can be adjusted .to the focus, the light concentrating point. or the point at which the light source is to be mounted, from the readings given by the finding apparatus.- The light source, a coiled metal fllameans of said apparatus is indicated directly or in I same relative value.

V stances, focus.

z-liable and four tests, each after 90 degrees of rotation of eitherthe reflecting. surface or the finding apparatus, are preferred. In such inaverage position is calculated for the Another modification of my invention isillustrated in Fig. 8 which makes use of a screen OI dividing the reflector ii in half. This modiflcation corresponds in a general way to that shown in Fig. 6 inthat'the point of concentration of the light is reached when the photoecell 80 receives the maximum amount of light. -The photo-cell ment inthe instance. shown, can thenbe mounted at the point indicated, either manually orwith the help of existing apparatus. a I To avoid the necessity of rotating the photo- 7 cells ll and II to cause them to scan the complete reflection ll, cylindrical photo-cells I5 and It as shown inFig. 5 can be used. The photo-cells II and I! are then mounted on a spindle ll located ,on the light projection axis of the reflector II in place of spindle and th adjustment thereof takes place in the manner previously described.

I "Another modification of the finding apparatus is shown in Fig. 6 which makes use of only a singlecyllndrical photo-cell II. This photo-cell 1| is relatively narrow, having a sensitive area of, for instance, only 1?; to of an inch in width and is manipulated by the spindle I! on which it is mounted until the greatest amount'of light is intercepted thereby. Thereilector-locating apparatus and the finding apparatus, except for the rotating means and the photo-cells MI and II of Figs. 1, 2 and 3, are preferably used in combination with the photo-cell 18.

3| is mounted behind the small circular opening II of limited area in the screen I! which is repositionedalong the axis of the reflector s I until the maximum amount of light passes through said opening l1 and the. maximum reading is gi'venby the milliammeter 88; It is preferred that four tests be made at 90 degree positions as in the prior instance and an average position be calculated. This apparatus as well as that shown l in Fig. 6 can also bowed to test the light ema reading.

ciency of the reflector'li' as the reading givenby the milliammeter 88 corresponds to the amount of light received by the photo-cells l6 and II.

A thermo-couple-or some other form of heat sensitive means can be used in place of the photocells in the apparatus disclosed with equally good results but a gr'eater time interval is required for It will be obvious that it is important that the portion of the focus locater which is actually at the focus of the reflector when the device is properly positioned must have a small area in order that the device be accurate. This portion.

. which is referred to in one of the claims as the "reference portion," is the narrow uncoated space between surfaces 40 and 4| in Fig. 4, the corresponding space between surfaces "15 and 16 in Fig. 5, the surface I8 itself in Fig. 6, the shield II in Fig. 7, and the opening 81 in Fig. 8.

a What I claim as new and desire to secure by In the flrst two species described above, the

function of the photo-cells lit-ll and 15-" is to intercept the light above and below arelatively narrow band establishedby the'division between photo-cells and is much the same as the modiflcation shown in Fig. 7 although here the nonlight-sensitive area has appreciable width.

This

particular construction allows a photo-cell 80 of commercial size to be used but is only adapted to test one-half of the reflecting surface II at one time. A relatively small round opaque screen I! of limitedarea is preferably mounted at the cen- Letters Patent of the United States is:

l. The method of determining the proper position for a light source in a reflector which comprises directing light into said reflector at the same angularity to the light projection axis thereof as that desired of the light to be projected thereby when said light source is in 'position, and

iinding a limited area along said axis where the redirected light passing'thereabout is a minimum by placing a screen of limited area in a plane passing through said projection axis with a light-- sensitive cell held behind said screen and then' moving said screen along said axis within the reflector until the light falling on said cell is a minimum. 7

2. The method of determining the proper position for a light source in a reflector which come prises directing light into said reflector at the same angularity to the light projection axis thereof as that desired or the light to be projected thereby when said light source is in position, and

axis of projection comprising a pair of Cylindrical alignment with each other finding the point of concentration of the redirected light from an angularly restricted area or the reflector about-the said axis by moving along said axis a screen member located in a plane passing through said axis within the reflector with a light-sensitive cell held behind said screen.

3. The method of determining the proper position for a light source in a reflector which comprises directing light into said reflector at the same angularity to the light projection axis thereof as that desired of the light to be projected thereby when said light source is in position, and finding the point of concentration of the redirected light from each of a plurality of angularly restricted areas of the reflector about the said axis to determine an average'position for the light source by moving along said axis, in a plurality of different angular positions, a screen *member located in a plane passing through said axis within the reflector with a light-sensitive cell behind said screen.

4. Apparatus for determining the proper position for a light source in a reflector having an axis of projection comprising a pair of photocells mounted closely adjacent and in alignment with each other in the direction of said axis of projection, means for definitely positioning said reflector with relation to the photo-cells and aligning its light projection axis therewith, means for directing light onto said reflector at the same angularity to its light projection axis as that desired of the light to be projected thereby, means for permitting the adjustment of the photo-cells and said reflector with relation to each other along said axis and means connected to the photo-cells for indicating the proportionate amounts of light intercepted thereby so that the relation of each photo-cell to the point of concentration 01' the light redirected by the reflector is indicated.

5. Apparatus for determining the proper position for a light source in a reflector having an axis of projection comprising a pair of photocells mounted closely adjacent and in alignment with each other in the direction of saidaxis of projection, means for definitely positioning said reflector with relation to the photo-cells and aligning its light projection axis therewith, means for directing light onto said reflector at the same angularity to its light projection axis as that desired of the light to be projected thereby, means for rotating the photo-cells on the light projection axis to permit them to intercept light from all portions of the reflector,

means for permitting the adjustment of the photo-cells and. said reflector with relation to each other along said axis and means connected to the photo-cells for indicating the proportionate amounts of light intercepted thereby so that the relation of each photo-cell to the point of concentration of the light redirected by the reflector is indicated,

6. Apparatus for determining the proper position for a light source in a'reflector having an tionate amounts of light intercepted thereby so that the relation of each photo-cell to the point of concentration of the light redirected by the reflector is indicated.

7. Apparatus for determining the proper position for a light source in a reflector having an axis of projection comprising means for holding the reflector in a definite position, means for directing light onto said reflector at the same angularity to its light projection axis as that desired of the light to be projected thereby, a shield of limited area arranged to be located in a plane passing through said projection axis and to be moved relatively to the reflector along said projection axis of the reflector, light-sensitivemeans mounted to one side of said shield in a position to receive the light from the portion of the reflector on the opposite side thereof and not intercepted thereby, and means for indicating the amount oflight falling on said light-sensitive means during movement of said shield along said axis so that the relation of the shield to the point of concentration of the light redirected by this portion of the reflector is indicated.

8. Apparatus for determining the proper position for a light source along the axis of pro jection of a parabolic reflector comprising a pair of photo-cells mounted closely adjacent and in alignment with each other in the direction of said axis of projection, means for definitely positioning said reflector with relation to the photothe said photo-cells so that their relationto the focus .is indicated,

9. Apparatus for ascertaining the focus of a concave reflector comprising means for support-. ing the reflector, means for directing into said reflector a light beam which is angularly similar to the beam for which the reflector was designed but opposite in direction, a light-sensitive device mounted so as to be located within the reflector, said light-sensitive device comprising a conductive base member extending along thelight-projecting axis of the reflector and having light sensitive coatings thereon above and below a'narrow uncoated space, said reflector supporting means and said light-sensitive device being arranged for relative movement along the said axis of the reflector, and means electrically connected to the said light-sensitive surfaces for indicating the proportionate amounts of light interceptedsaid suriacesare receiving equal amounts at light..

10. Apparatus for ascertaining the icons of a concave reflector comprising means for supporting the reflector, means for directing into said reflector a light beam whichis angularly similar to the beam for which the reflector was designed but opposite in direction, focus locater means including light-sensitive means, electric current measuring means connected to said light-sensitive means, said locater means having a reference portion thereof of very small area said locater 7 means and said reflector supporting means being arranged for relative movement of said reference portion oi the locater means along the axis of the reflector and through its focus. said reference portion of the locater means being arranged sothat when properly positioned it is in the path or light converging at the focus 0! the reflector from points both ahead of and behind its focal plane so that a distinctive reading is obtained 1 on said current measuring means.

EINAR JOHN WESTERLUND. 

